Method of producing cellulose fiber



Continuation of application Serial No. 135,023, filed December 4,1916. This application filed October 21,

- Serial No. 232,274. s

"sidin UNITED STATES.

PATENT OFFICE.

Jonson DE cnw, or nnw YORK, 1v. Y.

METHOD OF PRODUCING CELLULOSE FIBER.

T 0 all whom it may concern Be it known that I, JUDsoN v a citizen,of the Dominion of Canada, re-

at 501 Fifth Avenue, New York, N.- have invented new and useful Improvements in Methods of Producing Cellulose Fiber, of which the following is a specification.

This invention relates to the prodifction of the cellulose fibers by means of alkaline materials, and is a continuation of" my application Number 135,023, filed December 4!, 1916. The present method of making cellulose fiber from woodor ligno-cellulose material by means of caustic soda, orv sodium sulfid solutions, is to treat the material with dilute alkaline solutions under heat and pressure within a digester. The alkaline material, according to present methods, is never sufficiently concentrated to effect a resolution of the material without circulation of the alkali through the material, so that by accelerating the rate of diffusion, the internal portions of the chips may be finally reduced. The circulation of the solutions is so important that some of the more recent processes that have been introduced are those by means of which the results are imr proved by increasing the circulation as much as possible.

- The object of this invention is to go a step farther and not only avoid the necessity for liquor circulation but to obtain a uniform attack on all the fibers simultaneously.

-In order to do this, it is necessary to impregnate the chips with a hot alkaline solutionhaving sufficient temperature and concentration to immediately combine with the lignocellulose and liberate the cellulose fibers.

'All the older methodsof cooking contemplate either treatment with alkaline liquors too weak to effect immediate resolution of the wood or else the wood is impregnated .with cold solutions and then gradually heated.

-'By either method the fibers on the outside of the chips will be over-cooked anc consequently weaker and inferior in charac 'ter than the rest of the pulp.

There is only one way thatuniform action upon the fibers can be obtained and thatis to treat them with liquors alreadyprepared at the. right concentration and temperature to dissolve thewood. The ac- Specification of Letters Patent.

A. DE CEW,

,.ing the chips to drain.

, Patented Oct. 5, 1920.

tion in this case is immediate, so the cooking time is not delayed through the necessity of Waiting for the free alkali in the surrounding solutions to work its way into the wood which take time and roduce unequal dilution of the alkali. eating the liquors in the digester also'slows up the cooking action by dilution resulting from the condensed steam. I

An example of the operation of this process is as follows :An alkaline solution is prepared containing approximately 15% caustic alkali. This may consist either mainly of caustic soda or a mixture of caustic soda or sulfids. The exact concentration will depend on the porosity of the wood and the percentage of lignone it contains, there being a certain definite ratio by which the alkali and lignone must combine in order to liberate the fibers and not dissolve the cellulose.

The concentration of the alkali used, therefore, may vary from 15 to 20%, available alkali calculated as NaOH. This liquor is heated within a boiler to a high temperature and then discharged into a digester already charged with chips. (In common practice the. chips are covered'with cold alkali and then heated) The hot alkali solution is -or for heating up cold solutions, -both of soon as thechips are saturated, the excess alkali is withdrawn for further use, allow- The temperature within the digester is maintained for a short time and then the chips may be discharged in the form of pulp.

The result of this method reduces the cooking time to a minimum and also gives a maximum yield to the fibers. Inasmuch as all the cellulose fibers are liberated at the.

sametime there is no opportunity for the fibers of the smaller chips to be dissolved by the free caustic while the larger chips are undergoing a slow "cooking action, asctakes place in common practice. f

With proper chemical control of this process in which the temperature andconcentration are exactly determined and regulated for each character of wood treated, it

is possible to effect practically immediate resolution of the wood into cellulose so that the entire operation of charging, cooking and discharging the digester may not take more than one hours duration.

Another advantage of this process is that the oxidation taking place in the longer cook is correspondingly reduced by the reduction in cooking time.

What I claim is: 1. A method of making cellulose fiber which consists in impregnating ligno-cellulignone will be attacked only by-the alkali absorbed. 2. A method of making cellulose fiber which consists in preliminarily heating a caustic alkaline solution to a plup cooking temperature, discharging the hot solution into a digester containing the chips to be acted upon, withdrawing the excesssolution of alkali as soon as the chips are saturated, and then discharging them therefrom as pulp.

3. The method of claim 2 in which the solution contains approximately 15% caustic alkali.

4t. A'method of making cellulose fiber which consists in impregnating chips with enough caustic at pulp cooking temperature to effect resolution of the cellulose and then withdrawing the excess liquor.

In testimony whereof, I have signed my name to this specification this th day of October, 1919.

JUDSON A. DE cnw. 

